1. Field of the Invention
The present invention relates to a scanner and a control method for controlling lighting a cold-cathode tube which is a light source of the scanner.
2. Description of the Related Art
FIGS. 4A and 4B show the configuration of a conventional type scanner connected to a computer and others and used for a reader for reading an image on a manuscript.
As shown in FIG. 4A, in the conventional type scanner 1, an image sensor not shown for reading a manuscript 50 is installed so that it can indirectly read the manuscript via a lighting plate 52.
Also, a cold-cathode tube, for example, a cold-cathode fluorescent lamp 20 is mainly provided between the lighting plate 52 and the manuscript to enhance resolution when the manuscript 50 is read and a pre-heater 30 is provided for pre-heating the cold-cathode fluorescent lamp 20.
Referring to the drawings, the cold-cathode fluorescent lamp 20 and the pre-heater 30 will be described below.
FIG. 4B is a sectional view showing the configuration of the cold-cathode fluorescent lamp of a scanner shown in FIG. 4A.
As shown in FIG. 4B, the cold-cathode fluorescent lamp 20 is formed by applying fluorescent paint to a part of the inner wall of a bulb 2a made of quartz and depositing or applying reflection coatings 2b and 2c on the outside face corresponding to the applied area of the above bulb 2a. Hereby, the cold-cathode fluorescent lamp has directivity of emitting all light emitted from the cold-cathode fluorescent lamp 20 from a radiation aperture 2d provided by the reflection coatings 2b and 2c. The pre-heater 30 for preheating the cold-cathode fluorescent lamp 20 to predetermined temperature is attached to the whole surface of the reflection coating 2c.
Even if the cold-cathode fluorescent lamp 20 is used under a low-temperature condition, luminance to an extent required for a light source for scanner can be acquired by energizing the pre-heater 30 and increasing the surface temperature of the cold-cathode fluorescent lamp 20 up to approximately 50.degree. C. by the pre-heater 30.
The conventional type scanner has the following problems.
The cold-cathode fluorescent lamp used in the conventional type scanner has a defect in a temperature characteristic that the quantity of light and the luminance of the cold-cathode fluorescent lamp do not become stable unless fixed time elapses after the cold-cathode fluorescent lamp is lighted because gas filled inside is not stable at low temperature.
The above characteristic causes a defect that unless only the cold-cathode fluorescent lamp is lighted beforehand and normal reading operation is started after time elapses to some extent if a scanner is used, an image sensor cannot fetch a stable image.
Also, to supplement the above defects, there is a method of always lighting only the cold-cathode fluorescent lamp even while a scanner is not used and immediately realizing normal operation when an image is read; however, there is a defect that as the cold-cathode fluorescent lamp is lighted even when a scanner is unused, power is often uselessly consumed.
Also, only when a manuscript is scanned, the cold-cathode fluorescent lamp can be immediately lighted by providing the above pre-heater and always heating the cold-cathode fluorescent lamp in place of always lighting the cold-cathode fluorescent lamp. However, in this case, as the pre-heater is driven as long as the power source of the scanner is turned on, power is greatly wasted.